1. Field of the Invention
Aspects of the present invention relate to a power supplying apparatus and a power supplying method, and more particularly, to a power supplying apparatus and a power supplying method which protect a circuit safely against over-voltage and over-current.
2. Description of the Related Art
A power supplying apparatus supplies proper power necessary to operate a circuit apparatus such as a computer system. Such circuit apparatus often needs direct current power as power, and consequently the power supplying apparatus rectifies input alternating current power and outputs direct current power.
Where the power supplying apparatus uses commercial alternating current power as an input, the input voltage may be a voltage such as 110V or 220V. Therefore, in order to accommodate both 110V and 220V input voltages, the power supplying apparatus uses the input 220V voltage “as is” and the input 110V input is doubled. Such a conventional power supplying apparatus is illustrated in FIG. 1.
The power supplying apparatus shown in FIG. 1 includes a rectifying part 12, a voltage selector 13, and a smoothing part 15. The rectifying part 12 includes diodes 12a, 12b, 12c and 12d and rectifies input alternating current power 11. The smoothing part 15 includes capacitors 15a and 15b that correspond to the input power 11 of 110V and 220V, for example, and charges energy of the current rectified by the rectifying part 12 into each capacitor 15a and 15b. 
The voltage selector 13 is disposed in a predetermined current path between the rectifying part 12 and the smoothing part 15, and serves as a switch to pass or interrupt the current. As shown in FIG. 1, if the voltage selector 13 is open, a voltage proportional to a magnitude of the input power is charged in the series combination of the capacitors 15a and 15b. However, if the voltage selector 13 is closed, a voltage proportional to a magnitude of the input power voltage is charged in each of two capacitors 15a and 15b. In this case, a voltage corresponding to double the magnitude of the input voltage is charged into the series combination of capacitors 15a and 15b. That is, where the input voltage is 110V, the power supplying apparatus outputs a direct current voltage proportional to double the input voltage.
However, although the input voltage is 220V, the voltage selector 13 may be closed due to a user's mistake or erroneous operation of the apparatus. In this case, the capacitors 15a and 15b may be damaged due to a voltage 1.4 times 220V being applied to each of the capacitors 15a and 15b. 
The power supplying apparatus 1 universally uses a switch-mode power supply (SMPS) which is advantageous in terms of efficiency. The switch-mode power supplying apparatus 1 further includes a MOSFET 17a, a transformer 18, and diodes 19a and 19b. The power supplying apparatus 1 converts a magnitude of the voltage applied to the smoothing part 15 through the transformer 18 to output a voltage Vo with turning on and off the MOSFET 17a using pulse width modulation (PWM).
According to the switch-mode power supplying apparatus 1, if the voltage selector 13 is closed due to user's mistake and an input voltage of 220V is supplied, an over-current may result in the MOSFET 17a, potentially resulting in an explosion. Further, even if the input voltage is applied consistent with the position of the voltage selector 13, if a problem related to feedback loop occurs upon operating the PWM or gate on time in the MOSFET 17a is raised due to degradation of a PWM controller IC, the MOSFET 17a may be also damaged.